What is a special building overlay?

A special building overlay is a Victorian planning control over land in towns and suburbs that stormwater can flood when a big storm overwhelms the drains. It does not stop you building. It means most new buildings and works on the mapped land start with a planning permit, and the authority that looks after the drains has a say on the floor level and on where the water goes.

Why is my property in a special building overlay?

The mapping comes from modelling how water behaves when the pipes under a suburb are full. It follows the low line of the land, and often an old drain, so it can cross backyards a long way from any creek. Often only part of a lot is shaded, and the planning control applies to that land. The council’s planning map or a planning property report shows the extent. The post on flood overlays covers overland flow in general.

How is it different from other flood overlays?

Victoria’s other flood overlays mostly deal with water from rivers and creeks, or the deepest and fastest water of all. This one deals with the urban drains. A lot can carry more than one, and the same structure can be read against each. The post on planning overlays explains how overlays sit over the zone.

What work needs a planning permit?

The overlay reaches buildings and works, which takes in extensions, sheds, carports, garages, raised floors and fences. It lists some minor work that may be exempt, and the council’s schedule to the overlay can change that list, so read both before you assume anything. The usual exemptions for small structures do not settle it alone. The post on the planning permit and the building permit covers how the two fit together.

What does the drainage authority look for?

The application goes to the council, which refers it to the authority that manages the drains. That is often a water authority across metropolitan Melbourne and the council itself in other places. Ask it for the flood level at your lot early, because the design hangs off it. It usually looks for:

a floor set above the flood level by the margin it asks for
open fencing that lets water pass
a flow path kept clear of walls, fill and stored goods
safe access to the building during a storm

Its answer can become a condition on the permit. On land treated as liable to flooding, the building surveyor may also need the council’s report and consent on the floor level before the building permit is issued.

Reading it for your own lot

RapidSiteplan reads the council and building rules for your lot from its address, checks the design against them as you place it, lets you edit it as often as you like, and prints the site plan. Site plans and assessments in minutes. Where the overlay is mapped, it is shaded over your lot, so you can see which part of the block is affected before you settle where the structure goes.

Search your address, or see what the plan shows for a shed, carport or other outbuilding. The Casey page lists what we hold for that council, and site plans by council covers the rest of Australia, with the Victoria page for the state.

Common questions

What is a special building overlay? It is a Victorian planning control over land in towns and suburbs that stormwater can flood when a big storm overwhelms the drains. Most new buildings and works on the mapped land start with a planning permit, and the authority that looks after the drains has a say.

What does the SBO overlay mean for a shed or a patio? A shed, carport, enclosed patio or fence on the mapped land can need a planning permit, unless the overlay or its schedule lists that work as exempt. The council or the drainage authority can then set the floor level and ask for open fencing or a clear flow path.

Does the special building overlay in Victoria stop me building? No. It sets the conditions the building has to meet, mostly a floor above the flood level and room for water to pass.